A mobile device is usually equipped with a card holder to facilitate placement of a phone card. However, due to a tolerance in a size of the phone card, the phone card may fail to be placed into the card holder. In order to avoid that situation, a size of a card groove of the card holder is usually larger than the size of the phone card, and the phone card is loose in the card holder, such that the phone card cannot be stably placed in the card holder when a user replaces the phone card, and the phone card is easily misaligned or dropped, resulting in a poor user experience of replacing the phone card.